In combined cycle single shaft power plants a key parameter in determining the optimum arrangement of turbines and generator on the shaft involves consideration of shaft torque, the layout and configuration of a heat recovery steam generator, that is typical component of a combined cycle power plant, as well a civil footprint.
With the availability of larger gas turbines limitations may be placed on existing clutches and bearing components and thus may result in a new need to find alternate turbine shaft arrangements.
A solution involves locating a steam turbine train between a gas turbine and generator. The limitations of this solution is that high torque is transmitted through the high pressure steam turbine.
Another solution involves locating a generator between a gas turbine and steam turbine and fitting a synchro-self-shifting clutch there between. For some installation, such clutches may not be available.